The present invention relates generally to medical devices and methods for providing differential perfusion. More particularly, the present invention pertains to novel cardiopulmonary bypass systems and to aortic catheter devices for establishing differential perfusion in a patient where selective hypothermia or hypothermia is desirable.
Partial or full cardiopulmonary bypass (hereafter xe2x80x9cCPBxe2x80x9d) support is needed for medical procedures requiring general anesthesia where lung function is to be arrested during routine and high-risk cardiovascular, cardioneural, neurovascular and other surgical interventions including beating, fully arrested or partially arrested cardiac procedures, to maintain cardiovascular, cardioneural and corporeal support of the respective heart, cerebral and corporeal organ systems. Such surgical interventions include treatment of aneurysms, congenital valve disease, and coronary artery disease.
In procedures where the heart is to be fully or partially arrested, it has been conventionally preferred that the heart and coronary vasculature be isolated from the rest of the cardiovascular system by application of an external cross clamp or side biting clamp. Isolation allows antegrade or retrograde perfusion of cold, warm ornormothermic oxygenated blood cardioplegia or crystalloid cardioplegia to the coronary arteries to aid in the preservation of the myocardium and to prevent dispersion of cardioplegia to the rest of the body. The heart chambers may then be vented for decompression and to create a bloodless surgical field for intracardiac interventions. For rapid cooling and arrest of the myocardium in open-chest procedures, direct application of a topical ice slush or cold pericardial lavage into the thoracic space is performed simultaneously while the cold coronary perfusion process is being accomplished.
One preferred way to accomplish CPB is to insert a venous cannula into the venous system, to withdraw deoxygenated blood into an extra corporeal circuit. A pump circulates the withdrawn blood through a blood oxygenator, heat exchanger and filter apparatus. The blood is then delivered to an aortic perfusion catheter that is inserted in the aorta of a patient.
Although CPB has been a valuable technology enabling surgical interventions, stroke and neurological deficit have been a well documented sequel as associated with the above described procedure. Recent literature has documented that the incidence of stroke is as high as 6.1% with an additional 30-79% of patients suffering from some form of cognitive deficit. Neurological deficit varies from patient to patient, however common injuries include: loss of memory, concentration and hand-eye coordination, and an increase in morbidity and mortality. The impact on the patient is significant, but factors such as age, the level of intellectual activity and the amount of physical activity pursued by the patient prior to surgery all affect the quality of life. Finally, patients who suffer from neurologic injury have a substantially prolonged hospital stay, with an attendant increase in cost (Neurological Effects of Cardiopulmonary Bypass; Rogers AT, Cardiopulmonary Bypass Principles and Practice; Gravlee GP, 21:542).
One of the likely causes of stroke and neurological deficit is the release of emboli into the blood stream during heart surgery. Potential embolic materials include atherosclerotic plaques or calcific plaques from within the aorta or cardiac valves and thrombus or clots from within the chambers of the heart. These potential emboli may be dislodged during surgical manipulation of the heart and the ascending aorta or due to high velocity jetting (sometimes called the xe2x80x9csandblasting effectxe2x80x9d) from the aortic perfusion cannula. In addition, application and release of an external cross clamp or side biting clamp has been shown to release emboli into the blood circulation. Other potential sources of emboli include any contact of the vessel walls with medical devices that have been introduced into the aorta. Additional sources of emboli include gaseous micro emboli formed when using a bubble oxygenator for CPB and xe2x80x9csurgical airxe2x80x9d that enters the heart chambers or the blood stream during surgery through open incisions or through the aortic perfusion cannula.
In an effort to reduce the deleterious effects of CPB and median sternotomies there has been much development in the area of minimally invasive cardiac surgery (MICS) to avoid the complications of CPB and the use of balloon catheters to address the clinical problems associated with a conventional median sternotomy and the attendant use of a cross clamp to occlude the ascending aorta. For example, U.S. Pat. No. Re. 35,352 to Peters describes a single balloon catheter for occluding a patient""s ascending aorta and a method for inducing cardioplegic arrest. A perfusion lumen or a contralateral arterial cannula is provided for supplying oxygenated blood during cardiopulmonary bypass. U.S. Pat. No. 5,584,803 to Stevens et al. describes a single balloon catheter for inducing cardioplegic arrest and a system for providing cardiopulmonary support during closed chest cardiac surgery. A coaxial arterial cannula is provided for supplying oxygenated blood during cardiopulmonary bypass. The occlusion balloon of these catheters must be very carefully placed in the ascending aorta between the coronary arteries and the brachiocephalic artery, therefore the position of the catheter must be continuously monitored to avoid complications. Nonetheless, the deployment of balloons within the aorta may cause substantial forces to come to bear on the surrounding vessel and any shifting of such balloon may further increase the risk of dislodging embolic materials.
In clinical use, these single balloon catheters have shown a tendency to migrate in the direction of the pressure gradient within the aorta. More specifically, during infusion of cardioplegia, the balloon catheter will tend to migrate downstream due to the higher pressure on the upstream side of the balloon and, when the CPB pump is on, the balloon catheter will tend to migrate upstream into the aortic root due to the higher pressure on the downstream side of the balloon. This migration can be problematic if the balloon migrates far enough to occlude the brachiocephalic artery on the downstream side or the coronary arteries on the upstream side.
Another important development in the area of aortic balloon catheters is the concept of selective aortic perfusion. Described in commonly owned U.S. Pat. Nos. 5,308,320, 5,383,854 and 5,820,593 to Safar et al. is a method and apparatus for selective perfusion of different organ systems within the body. Other U.S. patents which address the concept of selective aortic perfusion include; U.S. Pat. No. 5,738,649, by Macoviak, U.S. Pat. Nos. 5,827,237 and 5,833,671 by Macoviak et al.; and commonly owned, copending U.S. patent application Ser. No. 08/665,635, filed Jun. 18, 1996, by Macoviak et al. All the above listed patents and patent applications, as well as all other patents referred to herein, are hereby incorporated by reference in their entirety.
Disadvantages associated with heretofore known devices and methods for establishing differential perfusion include the difficulty inherent in deploying numerous, complex devices in the vasculature, maintaining such devices in position during the procedure, avoiding the dislodgment of embolic materials and possibly the need to take steps necessary to recapture any such materials downstream. An improved device and method is needed that simplifies the deployment procedure and the efforts needed to maintain the device or devices in position while greatly reducing if not substantially obviating the risk of dislodging embolic materials. Although the foregoing discussion is primarily focused on stopped heart procedures, the present invention also has applicability in beating heart procedures including cardiac surgery and stroke.
In keeping with the foregoing discussion, the present invention provides devices and methods for establishing differential perfusion and overcomes some of the disadvantages associated with other known devices and methods. More particularly, the present invention allows for differential perfusion of circulatory subsystems by establishing differentiated blood flows without the need to deploy occlusion balloons or other flow separators. By eliminating the presence of such devices in the blood vessel, direct contact with the walls of the vessel is avoided and thus, the risk of dislodging embolic material is reduced.
Differential perfusion is achieved in accordance with the present invention by carefully adjusting the flow rates of blood delivered through multiple lumens, which have exit ports positioned in a spaced apart relationship within a blood vessel. By adjusting the relative flow rates of the two lumens a zone of zero average flow velocity is created. This zero average flow velocity or inversion layer demarks the effective separation of the two flows which may be differentiated in terms of any of a number of parameters including but not limited to temperature, degree of oxygenation or pharmacological content which is specifically altered for the purpose of providing optimal flow requirements to the targeted subsystem.
In the preferred embodiments, two lumens are positioned in the aorta such that one exit port(s) is positioned in the aortic arch and the other exit port(s) is positioned in the descending aorta. By adjusting the relative flow rates through the two lumens, either through manipulating the flows of an external pump, clamping output channels or by lumen size and output configurations, an inversion layer is established downstream of the left subclavian artery. The cerebral and corporeal subcirculation effectively become segmented to facilitate the differentiated support of such subsystems. Optionally, a third lumen can be positioned in the vena cava or right atrium to serve as a means for withdrawing deoxygenated blood from the patient for reoxygenation and differential reconditioning which will be returned to the aorta through the two lumens of the aortic catheter(s). The present invention contemplates the use of a single blood pump and at least one heat exchanger, at least one oxygenator and various inline arterial filters. By employing a single pump, the complexity of the system is greatly reduced and equalization of output pressures is more easily attainable. Unique pumping systems can be used to attain desirable results. For example an integral heat exchanger and oxygenator located before or after separation into arch and corporeal flows can be used with an addition heat exchanger for the arch circulation. The temperature of withdrawn deoxygenated tepid blood is easily adjusted through a heat exchanger and oxygenator to achieve the desired differentiation.
Various catheter configurations may be employed to achieve the desired placement in the aorta. For example, a single catheter comprising two lumens or two catheters having a single lumen may be employed to deliver the two differentiated flows to the aorta wherein the single device configuration allows for a constant distance separation of the exit ports, while the latter configuration has the additional benefit of allowing the relative spacing of the two sets of exit ports to be altered in an effort to more readily accommodate variations in patient anatomies. The catheters may be introduced peripherally, for example the femoral, brachial, iliac, subdlavian, radial or carotid artery, through an intercostal space or centrally via an aortotomy, or via a combination of both.
After proper placement is verified through the use of TEE, transillumination, infrared or other means, the surgeon generally begins CPB and starts perfusing the aorta prior to application of an external cross-clamp or internal cross-clamp to the ascending aorta. Once minimum proper perfusion flow has been established the surgeon will apply the cross-clamp to the aorta or use a valve or inflate an occlusion balloon inside the aorta and supply crystalloid cardioplegia or blood cardioplegia to the myocardium to completely or partially arrest the heart. By advantageously adjusting the relative flow rates through the two perfusion lumens or by adjusting their relative positions in situ or by predetermining out flow port position, an inversion layer is created just downstream of the left subclavian artery. The inversion layer can be moved either upstream or downstream by adjusting relative flow rates or by adjusting the relative positions of the lumens and outflow ports to achieve the desired position. For example, the inversion layer may form in the aortic arch creating superior flow to the arch vessels and inferior flow to the corporeal circulation. In one preferred embodiment, flow delivered upstream of the inversion layer, hypothermic oxygenated blood is perfused to the arch vessels through the arch perfusion ports. Downstream of the inversion layer, normothermic oxygenated blood is perfused to the corporeal circulation through the corporeal perfusion ports. Upstream of the cross-clamp or occlusion balloon, cardioplegia is supplied to keep the heart in a partially or completely arrested state.
By establishing differential perfusion in accordance with the present invention, the clinician is able to isolate the cerebral circulation from the corporeal circulation and thereby facilitate the creation of a neuroprotective environment through temperature, pressure and chemical control, allowing the brain to be cooled to a significantly lower temperature than the body. Lowering the temperature of the brain allows the blood flow to the brain to be reduced since the metabolic demands of the tissue for oxygen are reduced. The reduction in flow, volume and cycles of blood to the brain provides less opportunity for emboli to be introduced into the cerebral blood circulation during surgical interventions. In addition, prolonged hypothermia for the brain while the body is warm extends the neuroprotective period while avoiding issues associated with systemic hypothermia, such as coagulopathy, low cardiac output and prolonged Intensive Care Unit time.
These and other features and advantages of the present invention will become apparent from the following detailed description of preferred embodiments which, taken in conjunction with the accompanying drawings, illustrate by way of example the principles of the invention.